This invention relates to packaging and, more particularly, to a process for making a unitary package which comprises a load that has a band formed of plural layers of a stretched material wrapped around it. The present invention is also concerned with the product produced by such a process and to certain apparatus which can be utilized to perform the process.
In the past, various methods and apparatus have been utilized to provide a unitary package comprising a load having at least a portion of its surface overwrapped by a heat-shrunk material. Such methods are commonly referred to as "shrink-palletizing" processes and basically comprise unitization of a palletized package load by first overwrapping it with a heat shrinkable material which is then tightly shrunk against the package load by applying sufficient heat to the overwrapped load to raise its temperature to the heat-shrinking temperature of the overwrapping material. Our U.S. Pat. No. 3,793,798, describes a recent and efficient form of such "shrink-palletizing" systems; while older forms thereof have been described in detail in U.S. Pat. Nos. 3,514,920; 3,581,458; 3,590,549; 3,626,654; 3,640,048; 3,662,512; and 3,670,880.
While the aforedescribed "shrink-palletizing" systems have produced a product which has been generally satisfactory, they require heating means and, if a portion of the overwrapped package load is removed after completion of the heating step, the remaining portions tend to become loosened since the overwrapping material becomes permanently set and loses its elasticity after the heating has been performed.
Previous attempts have been made to overcome these disadvantages of the "shrink-palletizing" systems by substituting non-heated overwrapping systems, such as that described in U.S. Pat. No. 3,495,375 and another marketed by Arenco Machine Company, Inc., of Teterboro, N.J. Such non-heated systems are commonly known as "stretch-palletizing" systems, wherein the package load is overwrapped by a single-layer band of stretchable material that is held in tension around the package load but not heat-shrunk to it. Although the cost of the heating means and step and the problems of loss of elasticity and load loosening which exist in the "shrink-palletizing" systems, have been eliminated these prior-art single-layer band "stretch-palletizing" systems have several disadvantages of their own. For one example, the trailing edge or edges of the band-forming overwrapping material must be fin-sealed (as opposed to lap-sealed) along substantially their entire width and this requires elaborate clamping and sealing means. For another, tension is not evenly applied to the material forming the overwrapping band. And, for yet another, the sharp edges of the surface of the overwrapped package load tend to pierce the single layer of the tensioned wrapper band as it is dispensed therearound.
The present invention is particularly concerned with providing an improved process for producing a unitary package, which is somewhat similar to the aforenoted single-layer "stretch-palletizing" systems in that it provides similar advantages over the aforedescribed "shrink-palletizing" systems, but which also eliminates the aforenoted problems which have heretofore plagued the earlier forms of "stretch-palletizing" systems.